The invention relates to a device for producing and/or for processing mixtures having several components, in particular plastic mixtures, the device comprising a mixing head with at least one inlet for the mixture or its components, with a rotatably driven mixer in the mixing head for mixing the mixture or its components and with an outlet for the mixture, whereas the mixer is arranged axially displaceable in the mixing head by means of a drive unit and releases or closes the outlet according to its axial position.
When processing plastic mixtures, for example for producing a seal moulded directly onto a valve lid, the individual components of the plastic mixture are to be mixed with one another, if possible, only immediately before the processing of the plastic material consisting of the several components. For the production and the processing of mixtures with several components, a typical device is known from DE-OS 42 35 850, in which the individual components of the plastic mixture to be processed are fed to a mixing head and are mixed therein by means of a rotating mixer. The final mixed mixture can leave the mixing head by means of an outflow and can be injected directly into a die or moulded onto a part, for example as a seal. With the known mixing device, the mixer serves also as a closing means for the outflow and can be axially displaced in the mixing head by means of a pneumatic cylinder which engages the mixer shaft, whereby the mixer closes the outflow in a valve needle-like manner in a first, lower position with an approximately conical point, and opens the outflow in a second, raised position so that the mixed plastics can be ejected.
This known device has proved to be very successful in practice, as the mixer does justice to its dual function on one hand as a mixing element, and on the other hand as a closing means, so that operation disturbances occur only rarely, and high qualities are achieved with the injected parts, in particular also with moulded-on seals. But it has been found that the sudden opening or closing movement of the mixer in the axial direction, when using the pneumatic cylinder acting immediately on the mixer shaft, results in a quality loss of the tools, seals or the like, which are produced from the mixture, when sensitive materials are processed. In consequence of the sudden starting and the very fast lifting of the mixer for opening the outlet, the volume in the mixing region of the mixing head is increased in a very short time to such an extent that, depending on the rheology of the produced mixture, or its components, these cannot flow fast enough from their inlet along the mixer side walls through the mixing region in the direction of the outlet, so as to fill the suddenly enlarged volume in this region. A low pressure can result from the sudden lifting of the mixer in the mixing head, in particular when the outlet is still filled with remainders of the mixture ejected from the previous processing. The low pressure in the mixing head can result, even though only for a short time, in an exhaling of the produced and processed plastic mixture in the mixing head, which results in a quality loss of the material to be processed or it does not have even processing qualities during the processing procedure. It can result that a part of a seal which is moulded onto a part by means of the device is foamed in a different way than the rest of the seal so that the complete seal does not obtain an even thickness and a reliable closure cannot be guaranteed with the seal which is being produced.
It is an object of the invention to improve a device of the above-mentioned type in such a way that a sudden opening or closing of the outlet opening by means of the mixer is avoided, and to thereby prevent the disadvantageous influences on sensitive materials which are to be processed. This object is achieved by means of the invention, in that the drive unit comprises a mechanical cam drive having at least one actuating cam which cooperates with a lifting element engaging the mixer or its shaft.
By the use of the cam gear, in which the actuating cam(s) lifts or lift the lifting element and therewith the mixer for opening the outlet, it is possible to increase the speed of the mixer during the opening from a very small value at the beginning of the lifting movement during the further course of the axial movement of the mixer. The cam drive permits the use of actuating cams with different cam areas, which can be adapted to the material and the flow behaviour of the material which is being processed in an optimal manner. As the opening speed of the mixer which closes the outlet in the manner of a needle valve is only small at the beginning of the opening movement, the mixture in the mixing head can readily fill the increasing volume in the mixing head during the critical opening movement, so that the mixer does not produce any low pressure by means of its displacement in the mixing chamber of the mixing head and the mixed mixture of several components which is to be processed cannot exhale and experience a quality loss. During the further course of the opening movement, in which the influence of the opening speed of the material which flows in the mixing head to the outlet is reduced noticeably and the danger of quality loss due to fast opening is not present, the opening speed will be increased considerably by correspondingly the formed actuating cam(s), so that the total time in which the outlet for the mixture with several components is released completely does not have to be larger than with the known devices, and a processing of the mixture can occur after the start of the opening movement of the mixer within the shortest time.
The cam drive has preferably at least one camshaft comprising an actuating cam, which shaft is mounted rotatably in a bearing housing at the side next to the mixer shaft. It is particularly suitable to provide a cam drive with two parallel camshafts each having an actuating cam, which camshafts are mounted rotatably in a common bearing housing on both sides of the mixer shaft. With this embodiment, the lifting element preferably engages the mixer shaft, so that the entire drive unit for the displacement of the mixture in its axial direction can be arranged away from the actual mixing head. Therefore, there is no danger that the drive unit contacts the mixture of the several components which is to be processed with its partially very precisely manufactured parts, which could lead to faults or inaccuracies when opening and closing the outlet. By the use of two parallel camshafts, which are preferably driven in a counter-rotating manner in the housing, it is ensured that the axial movement, which is produced when the cams during their rotation are hobbing at the lifting element, is introduced exactly axially into the mixer shaft so that this will not be cocked when the mixer is displaced. The camshafts suitably have a common drive element which ensures that the cams of both camshafts are always rotated by exactly the same amount and act evenly on the lifting element so as to lift the mixer in the mixing head or lower it when closing.
A particularly advantageous type of drive for the camshafts results when these are provided with a drive gear which can be rotated by a gear rack drive element which is driven in the axially displaceable direction. The gear rack drive element can be provided with a dual or peripheral gearing for both drive gears at the two camshafts which are preferably arranged in parallel. By the displacement of the gear rack drive element in its axial direction, the two drive gears of the camshafts and the actuating cams which are arranged thereon are preferably rotated in a counter-rotating manner, whereby the cams hob along the lifting element with their cam areas, and lift this or draw it back or lower it or move it forward, depending on the direction of the displacement of the gear rack drive element. A most advantageous design is that, in which the drive element consists essentially of the piston of a hydraulic or pneumatic piston-cylinder unit or is coupled thereto. The pressure which is exerted from the compressed air or the hydraulic fluid to the piston of the piston cylinder unit is transferred to the cam drive by the gear or by another suitable transfer element, and is converted into the uneven opening movement which lifts the mixer with an increasing speed from the outlet.
When using a piston-cylinder unit for the drive of the cam gear, a dual-acting cylinder can be used, to the cylinder chamber and to the annular chamber of which can be fed compressed air or hydraulic fluid so as to ensure the turning back of the cams for closing the outlet securely. A simpler but still very reliable design of the invention results when the drive element has a reset spring which is compressed during the opening movement of the mixer, and which returns into its original position for closing the drive element which it takes up when the outlet is closed. When the piston rod of the piston of a hydraulic or of a pneumatic cylinder is used as the drive element, the reset spring moves the drive element back automatically when the pressure in the cylinder of the piston-cylinder unit is reduced or cancelled.
So as to prevent that the reset spring, which is formed as a compression spring, bends to the side when compressed, the drive element preferably comprises an axial guide bore which receives the compression spring at least partially. The reset spring, which is formed as a compression spring, can, additionally to the guide bore or alternatively thereto, be wound around a guide mandrel which also ensures that the spring is only compressed or extended in its axial direction and that a lateral movement of the spring does not take place.
The actuating cam(s) preferably has/have a cam design with a steady or smooth course. Actuating cams designed in this way facilitate the lifting or withdrawing of the mixer in the mixing head with an evenly increasing speed without acceleration jumps, that is, without sudden movements of the mixer during the entire opening procedure, so that the volume in the mixing chamber increases continually and can be filled by the material to be processed without time delay. The actuating cams preferably have a cam radius which increases from the closed position to the position of the mixer which releases the outlet of the mixing head, whereby it is possible, with an even drive speed of the drive element, to increase the opening speed of the mixer continually when the outlet is opened or to decrease it from a high speed to a very low speed just before reaching the closed position when it is closed.
The actuating cams of the two camshafts arranged in parallel to one another are, as already mentioned, preferably arranged in a mirror-like image, and the corresponding camshafts are driven in a counter-rotating manner. The actuating cams can be arranged exchangeably at the corresponding camshafts, whereby it is facilitated that a simple exchange of only the actuating cams optimises the opening movement and the speed of the mixer for different mixtures to be processed. It is also possible to mount the complete camshafts exchangeably in the housing and to exchange them together with the actuating cams arranged thereon and possibly the drive gears with other camshafts, which offer advantages when a different material is processed.
The lifting element is preferably connected in the axial direction of the mixer shaft in an adjustable manner. The adjustable connection makes it possible to adjust the device in such a way that the actuating cam(s) in the closing position of the mixer do not have an immediate contact with the lifting element, so that it is ensured that the mixer closes the outlet completely with its tip. The lifting element can essentially consist of an actuating sleeve which surrounds the mixer shaft in a coaxial manner and a bearing reception for an axial bearing of the mixer shaft which is adjustably threaded thereto. The adjustability of the lifting element at the mixer shaft is facilitated by threading the bearing reception into or out of the actuating sleeve. The axial bearing, which transfers the axial movement which is exerted on the lifting element by means of the cams, and moves this thereby in the housing, consists preferably of a radial grooved ball bearing, which forms therewith at the same time the radial shaft bearing which is arranged at one end of the mixer shaft. The radial grooved ball bearing facilitates not only the rotation of the shaft around its own axis, but also allows the transfer of axial forces when the shaft is rotated for its displacement in the housing.
The lifting element can suitably be displaced axially in the housing by the actuating cam(s) against the force of a closing spring. The closing spring ensures a resetting of the lifting element and at the same time of the mixer for closing the outlet, when the actuating cams are turned back into their original position, which they inhabited before the opening of the outlet at the mixing head. The closing spring presses the mixer shaft and the mixer with its tip rigidly against the outlet and closes this reliably against the undesired exit of material which is still present in the mixing chamber.
A particularly simple and elegant design of the lifting element results when the bearing reception surrounds the mixer shaft in a sleeve-like manner and is provided with an outer thread, with which it is threaded into an inner thread which is provided at the actuating sleeve. The bearing reception can preferably be adjusted with regard to the actuating sleeve from the outside of the housing, for which it can be received in a guide sleeve in an axially displaceable manner, which is arranged rotatably in the housing, while the bearing reception is arrested in the peripheral direction with regard to the guide sleeve. When the guide sleeve is rotated in the housing, the bearing reception is also rotated with this design and can be threaded into the desired position into or out of the actuating sleeve. For arresting the bearing reception with regard to the guide sleeve, it is is preferably provided with at least one stopper pin which projects radially inwardly, which engages a groove which runs along the bearing reception in the radial direction. The bearing reception can move freely in the axial direction with regard to the guide sleeve, but it cannot rotate in the peripheral direction with regard to the guide sleeve. So as to easily facilitate a rotation of the guide sleeve from the outside of the housing, it is suitably provided with a tool connector which can be accessed from the outside of the housing.
A preferred design of the device according to the invention comprises at least one stopper element for the mixer or the mixer shaft. The stopper element limits the opening path which the shaft or the mixer has to cover for completely opening the outlet. The stopper element can be arranged in the head of a housing, with which the housing is closed at its end. The arrangement is preferably in such a way that the head of the housing forms a cylindrical reception for the upper or the rear end of the mixer shaft, whereby the reception has an inner thread, into which the stopper element is adjustably threaded. The adjustable arrangement of the stopper element in the head of the housing permits a change and an adaptation of the lifting path of the mixer, so that the size of the annular gap which is defined by the mixer tip and the outlet can be changed and adapted to materials having different properties. The mixer shaft preferably does not abut the stopper element, but the abutment takes place indirectly by means of the bearing reception. The closing spring can also be arranged in the head of the housing, whereby it acts on the mixer shaft or its bearing reception with its first end in the axial direction, and is supported on a spring stopper which is arranged in the head of the housing with its second end. It is particularly advantageous if the spring stopper is arranged adjustably in the head of the housing, for example like the stopper element which is threaded into the inner thread provided in the head of the housing. The first end of the closing spring can act on the mixer shaft by means of a spring plate which is supported on the bearing reception, which distributes the spring force evenly across the entire periphery of the bearing reception, and introduces it into the mixer as a purely centrally acting force.
The invention suggests a method for opening and closing a closing element in a device for producing and/or processing mixtures with several components, in particular for operating a device according to the preamble of claim 1, in which the closing element or the mixer forming it is first lifted slowly from the outlet opening during the opening for releasing an outlet, and is, with an increasing distance from the outlet opening, moved away therefrom increasingly faster, and in which, during the closing for shutting off the outlet, the closing element, which has a distance from the outlet opening, will initially be moved with a higher speed towards the opening, and with decreasing distance from the opening, when it is getting nearer thereto, the closing speed will be reduced. Such a method, which can be carried out in a particularly advantageous manner by means of the cam drive of the device according to the invention, but which can also be realised by means of another suitable drive means at the device, such for example a controlled hydraulic drive, facilitates a very gentle treatment of sensitive materials when they are processed in the mixing head, so that parts having a high quality can be produced by means of the method.